#include<cstdio>

int a[10001], HashTable[10001] = {0};
int main(){
	int n;
	scanf("%d", &n);
	for(int i = 0; i < n; i++){
		scanf("%d", &a[i]);
		HashTable[a[i]]++;
	}
	int ans = -1;
	for(int i = 0; i < n; i++){
		if(HashTable[a[i]] == 1){
			ans = a[i];
			break;
		}
	}
	if(ans == -1) printf("None");
	else printf("%d", ans);
	return 0;
}
